mux
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Re: Toyota Mirai Fuel Cell

Tue Jun 18, 2019 9:36 pm

SageBrush wrote:
mux wrote: All this being said, it seems like at least the Norway explosion had nothing to do with the pressure vessels and was 'just' a hydrogen explosion. This is a much better outcome than e.g. a pressure vessel failure, because hydrogen leaks can be designed against very easily (just ventilation and roof geometry to prevent build-up of hydrogen gas and the formation of an explosive atmosphere). They dodged a bullet here, unless they find more issues.
I understand why a leak might catch fire, but why would it explode ?
Hydrogen has an explosive mix over a very wide range of mixtures. In air, at 16-75% by volume it will explode, so a leak is very likely to cause an explosive atmosphere and, considering the activation energy of a hydrogen-air mixture is essentially zero, an explosion is quite likely.

Also @GRA: Qualitative arguments are not enough to attack a quantitative argument.

SageBrush
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Re: Toyota Mirai Fuel Cell

Wed Jun 19, 2019 6:05 am

mux wrote: Hydrogen has an explosive mix over a very wide range of mixtures. In air, at 16-75% by volume it will explode, so a leak is very likely to cause an explosive atmosphere and, considering the activation energy of a hydrogen-air mixture is essentially zero, an explosion is quite likely.
I'm under the impression that the Hindenburg (sp?) did not explode. Was the H2 concentration below ~ 16% ?
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stjohnh
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Re: Toyota Mirai Fuel Cell

Wed Jun 19, 2019 6:09 am

SageBrush wrote:
mux wrote: Hydrogen has an explosive mix over a very wide range of mixtures. In air, at 16-75% by volume it will explode, so a leak is very likely to cause an explosive atmosphere and, considering the activation energy of a hydrogen-air mixture is essentially zero, an explosion is quite likely.
I'm under the impression that the Hindenburg (sp?) did not explode. Was the H2 concentration below ~ 16% ?
We've all seen Hindenburg burning, didn't explode. Wouldn't it have been 100% hydrogen? I.E. not explosive.
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SageBrush
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Re: Toyota Mirai Fuel Cell

Wed Jun 19, 2019 6:23 am

stjohnh wrote:
SageBrush wrote:
mux wrote: Hydrogen has an explosive mix over a very wide range of mixtures. In air, at 16-75% by volume it will explode, so a leak is very likely to cause an explosive atmosphere and, considering the activation energy of a hydrogen-air mixture is essentially zero, an explosion is quite likely.
I'm under the impression that the Hindenburg (sp?) did not explode. Was the H2 concentration below ~ 16% ?
We've all seen Hindenburg burning, didn't explode. Wouldn't it have been 100% hydrogen? I.E. not explosive.
Yeah, thus my question to Mux. We share a basic hole in our physics I hope Mux will plug :)

If I am understanding him correctly:
For H2 concentrations in air over 16% the dt in Fdt is an explosive rate of combustion so the force is ~ proportional to the amount of H2 present. A FCEV tank is up to ~ 680x the pressure of ambient at sea level
2013 LEAF 'S' Model with QC & rear-view camera
Bought off-lease Jan 2017 from N. California
Two years in Colorado, now in NM
03/2018: 58 Ahr, 28k miles
11/2018: 56.16 Ahr, 30k miles
-----
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mux
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Re: Toyota Mirai Fuel Cell

Wed Jun 19, 2019 10:01 am

SageBrush wrote:
mux wrote: Hydrogen has an explosive mix over a very wide range of mixtures. In air, at 16-75% by volume it will explode, so a leak is very likely to cause an explosive atmosphere and, considering the activation energy of a hydrogen-air mixture is essentially zero, an explosion is quite likely.
I'm under the impression that the Hindenburg (sp?) did not explode. Was the H2 concentration below ~ 16% ?
The Hindenburg didn't have a good hydrogen-air mixture! It was a big bubble of hydrogen where the outside may have had some turbulent mixture that got near the explosive limits, but the inside was pure hydrogen. As it turns out, in order to explode, you really need both H2 and O2.

Also, hydrogen is REALLY buoyant. I've been an onlooker when we hydrogen-proofed our student project work area, and if you look at a hydrogen bubble with a thermal camera (it's slightly refractive), it races upwards, like 20+mph in a matter of a few yards of rise. Hydrogen also breaks up easily in the air, meaning the individual pockets of maybe-explosive mix can't really connect easily. This makes hydrogen very safe in the open air. But, of course, sitting against the ceiling of a workshop it's incredibly dangerous. Give it a few minutes to mix and you're almost guaranteed an explosive mix.

smkettner
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Re: Toyota Mirai Fuel Cell

Wed Jun 19, 2019 10:37 am

Oils4AsphaultOnly wrote:Great, so they've taken significant efforts to protect the fueling stations. That does nothing to help the over 6300 mobile high pressure tanks out in the wild now.
Even if it was a million to one for a tank failure.... can't imagine having 200 million of these tanks running around town and parked in garages etc.
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GRA
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Re: Toyota Mirai Fuel Cell

Wed Jun 19, 2019 4:43 pm

mux wrote: Also @GRA: Qualitative arguments are not enough to attack a quantitative argument.
Alone, no, but the two affect each other. If the quality is high the quantity may be less important. I expect China will act as the canary in the coal mine in this case, as they're likely to have a combination of high quantity and relatively low quality before anyone else.
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The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

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Re: Toyota Mirai Fuel Cell

Wed Jun 19, 2019 5:01 pm

smkettner wrote:
Oils4AsphaultOnly wrote:Great, so they've taken significant efforts to protect the fueling stations. That does nothing to help the over 6300 mobile high pressure tanks out in the wild now.
Even if it was a million to one for a tank failure.... can't imagine having 200 million of these tanks running around town and parked in garages etc.
As has been discussed at length before, humans are much better at reacting to immediate, spectacular threats even if of very low probability, than chronic, low key threats of high probability, e.g. people are much more likely to be worried about the risk of a low probability event like an airliner crash while being a life-long smoker, which has a risk factor for premature death multiple orders of magnitude higher.

According to WHO estimates, air pollution causes the premature death of 4.6 million people/year world-wide, (obviously not all of which is generated by cars). There are around 1.2 billion cars in the world so if all of them were H2 FCEVs, at an annual rate of 1 explosion/1 million vehicles, that would be 1,200 tank explosions/year, or the same number of deaths annually if there''s an average of one death per explosion. Which poses the greater risk?

In the U.S., deaths due to air pollution are said to have dropped to 71,000 annually by 2010*; the number I have for the size of the LDV fleet is a couple of years old, so probably higher now, but it was 252 million. Applying the same rate of tank explosions you mentioned, that would be 252 or the same number of deaths annually as above, versus some significant fraction of 71,000 deaths (presumably even less now due to the shift away from coal) due to air pollution. Again , which poses the greater risk?


*https://e360.yale.edu/digest/us-air-pol ... wo-decades
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

GRA
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Re: Toyota Mirai Fuel Cell

Wed Jun 19, 2019 5:20 pm

mux wrote:
SageBrush wrote:
mux wrote: Hydrogen has an explosive mix over a very wide range of mixtures. In air, at 16-75% by volume it will explode, so a leak is very likely to cause an explosive atmosphere and, considering the activation energy of a hydrogen-air mixture is essentially zero, an explosion is quite likely.
I'm under the impression that the Hindenburg (sp?) did not explode. Was the H2 concentration below ~ 16% ?
The Hindenburg didn't have a good hydrogen-air mixture! It was a big bubble of hydrogen where the outside may have had some turbulent mixture that got near the explosive limits, but the inside was pure hydrogen. As it turns out, in order to explode, you really need both H2 and O2.

Also, hydrogen is REALLY buoyant. I've been an onlooker when we hydrogen-proofed our student project work area, and if you look at a hydrogen bubble with a thermal camera (it's slightly refractive), it races upwards, like 20+mph in a matter of a few yards of rise. Hydrogen also breaks up easily in the air, meaning the individual pockets of maybe-explosive mix can't really connect easily. This makes hydrogen very safe in the open air. But, of course, sitting against the ceiling of a workshop it's incredibly dangerous. Give it a few minutes to mix and you're almost guaranteed an explosive mix.
When you say that you "hydrogen-proofed" your project area, do you mean that you made it impossible for H2 to escape? Because an
experiment designed to replicate the typical home garage found that it was essentially impossible for H2 to build up to flammable or explosive limits; the H2 escaped easily. I posted the link to that study in the H2 and FCEV topic a long time ago, but will try and find it. However, this paper apparently reaches different conclusions:
HYDROGEN RELEASE AND
COMBUSTION MEASUREMENTS IN A
FULL SCALE GARAGE
https://ws680.nist.gov/publication/get_ ... _id=905528

BTW, we should probably move this discussion to that topic, as it really belongs there rather than here.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

GRA
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Re: Toyota Mirai Fuel Cell

Wed Jul 17, 2019 5:08 pm

Per IEVS, Toyota sold/leased 166 Mirais in the U.S. in June.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

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